Method and apparatus for lining a pipe with a polymer linear

ABSTRACT

A method and apparatus for lining a pipe with a polymer liner in which the liner is pulled through a die to reduce the liner&#39;s diameter and through the pipe and on removal of the pulling load, allowing the liner to revert to at least the minimum internal diameter of the pipe, wherein the liner has a maximum diameter before entering the die and a minimum diameter in the die. The die having an aperture which is symmetrical with respect to a central, longitudinal axis and comprising in the direction that the liner is passed an entry, a throat and an exit. The diameter of the aperture decreasing over the entry to a minimum to the throat and increasing over the exit. The entry of the die, when viewed in a sectional plane extending longitudinally of the liner and containing the axis, is convex over substantially an entire axial length between where the liner first contacts the die and the throat, wherein the liner substantially continuously engages the die over substantially the entire axial length.

The invention relates to a method of and apparatus for lining a pipewith a polymer liner.

The method is applicable, for example, to lining a buried gas, water orsewage pipe. Such pipes are made of cast iron or steel or particularly,in the case of water, of asbestos cement or concrete for example, andparticularly cast iron pipes may be lined with bitumen or concrete.

In British Gas patent application GB-A-2186340 there is described amethod applicable to buried gas, water or sewage pipes in which a lengthof synthetic resin liner is heated, pulled through a die and through thepipe to be lined and pressurised to cause it to expand into engagementwith the internal wall of the pipe.

In U.S. Pat. No. 3,462,825 (Pope et al) there is described a methodapplicable to the lining of flexible or rigid pipes in the factory bypulling a liner through a die and through the pipe and then releasingthe liner pipe, whereupon the liner pipe expands into tight engagementwith the internal wall of the pipe. The pipe was of relatively smalldiameter, having an inside diameter of 2.06 inches (51.5 millimeters)and the liner pipe had an outside diameter of 2.3 inches (57.5 mm). Theliner pipe was relatively thin, having a wall thickness of 0.07 inch(1.75 mm) giving a Standard Dimension Ratio (SDR) of 33. The liner pipewas of fluorocarbon. In general, the outside diameter of the liner pipewas 10 to 15% greater than the inside diameter of the pipe to be lined.

In British patent specification No. 807 413 (Tubovit Societa per Azioni)there is described a method applicable to the lining of metal pipes inthe factory by pulling a heater line pipe through a die and through apipe to be lined, releasing the liner pipe, and heating the liner pipe.The die diameter is the same as the pipe to be lined or very slightlyless. The liner is of polyvinyl chloride very slightly larger than thepipe to be lined and is 3 mm thick or less. The liner is heated beforeor during the die reduction to a temperature at which it is relativelysoft and the force used to pull it through the pipe is only relativelylow.

In GB 2186340 such die swell as does occur after the main die iseliminated by the effect of the second die which makes the diameter ofthe throat, in each case, the diameter which does into the pipe. In U.S.Pat. No. 3,462,825 and GB 807 413, no die swell is shown and thediameter which goes into the pipe is the diameter of the throat. Dieswell is the increase in diameter which the liner undergoes afterpassing through the die.

Our patent No. EP-B-0341941 describes a method of lining a buried pipewith a polymer liner, which comprises pulling a length of liner througha die to reduce its diameter and through the pipe and on removal of thepulling load allowing the liner to revert to at least the minimuminternal diameter of the pipe, the liner having a maximum diameterbefore the die and a minimum diameter in the die, and the die having acentral, longitudinal die axis and comprising an entry and a throatwhich are symmetrical about said axis, the entry decreasing in diametertowards said throat characterised in that the die also comprises an exitwhich increases in diameter away from said throat and the liner havingan intermediate diameter after the die before the liner enters the pipe,the force of pulling being such as partially to restrain die swell ofthe liner after its emergence from the throat, and the liner bendinginwards before first contacting the die at the entry, then leaving theentry before continuously bending through its minimum diameter as itpasses the throat, and then undergoing die swell resulting in saidintermediate diameter, which enters the pipe.

In that method, the liner bends as it passes through the die.

The present invention modifies the invention described in EP-B-0341941in that the strain in the liner due to its bending is introduced intothe liner more gradually compared with the method described in EP0341941B. This is achieved using a die in which the entry is curvedinstead of straight.

Dies having curved internal working surfaces have been proposed inGB-A-807413, U.S. Pat. No. 2,249,510, FR-A-2096557 and AU-A-65481/74.However, none of these proposals resulted in a method of lining a pipeusing a polymer lining as proposed in the present invention. The methodsdisclosed do not deal with a polymer liner which exhibits die swell.

A method of lining a pipe with a polymer liner, according to theinvention, comprises pulling the liner through a die to reduce itsdiameter and through the pipe and on removal of the pulling loadallowing the liner to revert to at least the minimum internal diameterof the pipe, the liner having a maximum diameter before the die and aminimum diameter in the die and the die having an aperture which issymmetrical with respect to a central, longitudinal axis and comprisingin the direction in which the liner is passed, an entry, a throat and anexit, the diameter of the aperture in said direction decreasing oversaid entry to a minimum at said throat and increasing over said exit,the liner having an intermediate diameter after the die and before theliner enters the pipe, the force of pulling being such as partially torestrain die swell of the liner after its emergence from the throat andthe liner bending towards said axis and in so doing presenting a convexouter surface (when viewed in a sectional plane extending longitudinallyof the liner and containing said axis) and then the liner bending awayfrom the axis and in so doing presenting a concave outer surface (whenviewed in said plane), the liner continuously bending through itsminimum diameter as it passes the throat and thereafter undergoing dieswell resulting in said intermediate diameter, which enters the pipe,characterised in that the entry, when viewed in said plane, is convexover an axial length between where the liner first contacts the dieafter bending inwardly and said throat.

Apparatus for performing that invention, according to the inventioncomprises in combination upstream of the pipe a die having an aperturewhich is symmetrical with respect to a central, longitudinal axis andcomprising in the direction in which the liner is passed, an entry, athroat and an exit, the diameter of the aperture in said directiondecreasing over said entry to a minimum at said throat and increasingover said exit, said die being secured to the surface of the ground orbeing connected to the leading end of the pipe, guide means for saidliner, and downstream of said pipe winch means for exerting a pull on arope connected to the leading end of liner and guide means for saidrope, characterised in that the entry of the die is convex over an axiallength between where the liner first contacts the die after bendinginwardly and said throat of the die.

A method of lining a pipe with a polymer lining, and apparatus forperforming that method, will now be described by way of example withreference to the accompanying drawings, in which:

FIG. 1 is a vertical section through the ground showing the pipe to belined and showing the liner pipe in the course of being pulled throughthe pipe to be lined; and

FIG. 2 is an enlarged vertical section through the die and through theliner pipe as it is passing through the die.

The method of lining a pipe using a polymer liner pips is substantiallythe same as that described in EP-B-0341941 and the whole of the contentsof the specification of that patent are incorporated herein byreference. The description which appears in EP-B-0341941 may be taken asa description of the method used in the present invention except for thedifferent die used. A description of the die used according to thepresent invention appears herein.

The method is as shown in FIG. 1, for example.

From now on, the liner pipe will be referred to as "the liner" and thepipe to be lined will be referred to as "the pipe".

FIG. 1 shows a buried pipe 10, which in this case may be for example acast-iron gas main, with its ends 12,14 exposed at two excavations16,18. The pipe continues at 20,22 and pieces have been removed at theexcavations 16,18. Eventually, the whole pipe will be lined and theliner joined up to make a continuous main.

The liner 30 is made, for example, of polyethylene and is pulled by awinch 32 and cable 34 through a swaging die 36 and through the pipe 10.The liner 30 after emerging from the die 36 is guided by a roller 38 tofacilitate entry into the end 12 of the pipe 10. The die 36 is securedby members (not shown) driven into the ground. In another alternativeposition, the die 36 is supported by direct engagement with the end 12of the pipe 10, or with members engaging the end 12. The winch 32 alsohas to be secured by members (not shown) driven into the ground, or fromthe end of the pipe 14.

Prior to the operations shown in FIG. 1, the pipe was cleaned andchecked for internal size by suitable pigs passed through the pipe. Atthe same time, any protrusions were removed from within the pipe. Theliner was made up of lengths of liner above ground. The lengths of linerwere joined end to end by butt fusion and the external bead at eachfusion joint was removed or directly inserted from a coil of liner (thisbeing the case in sizes up to 180 mm, for example). A pulling cone wasattached to the leading end of the liner. The cable 34 was attached tothe end of a stiff rod and the rod was pushed through the pipe 10 fromthe end 14 to the end 12 until the cable end (at the trailing end of therod) emerged at the end 12. The cable 34 was disconnected and fedthrough the die 36 and attached to the cone on the liner. The winch 32was then operated to draw the liner through the die 36, with thelongitudinal extension of the liner being less than 10%, preferably 8%.

The operator of the winch keeps the winch turning at a constant rate, ornearly so. The rate of advance of the liner 30 may for example be 3meters per minute.

When pulling is completed, the liner is allowed to revert at least tothe minimum internal diameter of the pipe. The liner is cut leavingsufficient pipe to enable a suitable connection to be effected. Wherethe die engages the end of the pipe 10 or a member or members engagingthe end of the pipe 10, a split die is essential. The winch cable 34 isremoved from the liner 30 which is then cut to allow sufficient lengthto accommodate contraction as the liner reverts.

FIG. 2 shows the behaviour of the liner 30 as it passes through thesteel swaging die 36.

As is shown in FIG. 2, the liner 30 engages the die 36 at its entry 54,the liner wall 74 having bent inwardly to do so. As viewed in thesectional plane represented by FIG. 2 the liner presents a convex outersurface 72 during this stage of bending towards the axis 50. The liner30 bends away from the axis 50 and in so doing presents a concaveinterior surface at 76, as viewed in the same sectional plane. Then, thewall bends continuously through its minimum diameter as it passes thethroat 58, the outer surface remaining concave. The liner 30 after itleaves the die again bends away from the axis 50 presenting a convexouter surface as it does so. At the point 80 the diameter, which hasbeen increasing after the die, reaches a maximum value. This is definedas "die swell" which enters the pipe 10. After the point 80 the wall 74bends inwards very slightly to a lesser diameter some distance beyondthe region shown in the figure.

The exact amount of die swell is the difference between the diameter at80 and the minimum or throat diameter at 58 of the die 36.

The die swell has to be taken account of in choosing the parameters ofthe present invention. Thus, in this invention, it is the diameter ofthe liner, including die swell, which is chosen to be less than theminimum bore diameter of the pipe 10.

The pulling force is kept preferably at about half the yield strength ofthe liner, and the die 36 is dimension to ensure that the die swell isjust at the correct value. Preferably, the choice is made to allow theliner 30 to be pulled into the pipe 10 with a "window" to allow the pullto be stopped for say, for example, 30 minutes if necessary.

The die acts as a means of reducing the liner diameter through itsprofile and frictional resistance. Work on the liner is primarilybending.

The liner 30 (FIG. 2) approaches the die 36 and bends towards the axis50. The external surface of the liner 30 is convex as viewed in thissection.

Then, the liner 30 contacts the entry 54 of the die 36, the entry beingthe whole of the arcuate surface up to but not including the throat 58.It is not easy to differentiate these portions on the figure shown. Tomake it easier a radial line normal to the internal surface at thethroat 58 has been drawn on the figure. The entry 54 is the whole of theinternal arcuate surface of the die 36 to the left of the line A. Thethroat 58 is at the line A. To the right of the line A is the exit 60.

At about the region 90 the liner 30 reverses its bending and bends awayfrom the axis 50. In so doing it presents a concave outer surface.

The die 36, according to the invention, is different from the die shownin our patent EP-B-0341941 in that instead of having a straight sectionto the entry 54 at this point, the die 36 has an inwardly convex surface92. The inwardly convex surface 92 matches as far as possible the outerconcave surface of the liner 30.

The liner 30 contacts the die 36 for the first time at the point 100. Aline B normal to the die surface has been drawn on the figure. Comparedwith the method described in EP-B-0341941, the liner engages the diecontinuously up to the throat 58. Therefore, the strain introduced intothe liner 30 by the die 36 is introduced more gradually over the arc ofthe surface of the through aperture between the lines A and B ascompared with the method described in EP-B-0341941.

The dimensions shown in FIG. 2 are as follows:

L: 160 millimeters (nominal)

T: 140 millimeters

W: 10 millimeters

R: 30 millimeters

A second die, similar to that described but in which T=144 mm instead of140 mm was used to produce the following results:

    ______________________________________                                        Original Diameter  mm        ( 160.8  (a)                                                        "         ( 160.7  (b)                                     Diameter after die (while under                                                                  mm        ( 149.4  (a)                                     load) measured at 80                                                                             "         ( 150.4  (b)                                     Diameter after die with load                                                                     mm        ( 155.5  (a)                                     removed : after 1 hour                                                                           "         ( 155.6  (b)                                     Diameter after die, Final                                                                        mm        ( 156.7  (a)                                                        "         ( 156.8  (b)                                     Pulling Load       Tonnes    ( 2.63   (a)                                                        "         ( 1.99   (b)                                     % Axial Strain while under load                                                                            ( 8.1    (a)                                                                  ( 6.9    (b)                                     % Axial Strain with load removed :                                                                         ( 2.9    (a)                                     after 1 hour                 ( 2.7    (b)                                     % Axial Strain with load removed,                                                                          ( 2.1    (a)                                     Final                        ( 1.9    (b)                                     ______________________________________                                    

Using such a die, the following results were obtained performing themethod with the die and pipe (a) dry and (b) lubricated with water:

    ______________________________________                                        Original Diameter (mm)       ( 160.8  (a)                                                                  ( 160.7  (b)                                     Diameter after die (while under                                                                  mm        ( 145.6  (a)                                     load) measured at 80                                                                             "         ( 146.4  (b)                                     Diameter after die with load                                                                     mm        ( 153.1  (a)                                     removed : after 1 hour                                                                           "         ( 153.4  (b)                                     Diameter after die, Final                                                                        mm        ( 154.9  (a)                                                        "         ( 155.2  (b)                                     Pulling Load       Tonnes    ( 2.9    (a)                                                        "         ( 2.36   (b)                                     % Axial Strain while under load                                                                            ( 11.4   (a)                                                                  ( 10.0   (b)                                     % Axial Strain with load removed :                                                                         ( 4.6    (a)                                     after 1 hour                 ( 3.8    (b)                                     % Axial Strain with load removed,                                                                          ( 3.2    (a)                                     Final                        ( 2.7    (b)                                     ______________________________________                                    

All of those tests were performed at an ambient temperature of 18degrees Centigrade, no heat being applied to the liner pipe or die. Theliner pipe was made of PE-X grade polyethylene.

It is to be noted from those results that, as the load is reduced (eg bythe effect of lubrication) the diameter measured at 80 while the linepipe is still under load (ie the diameter of the liner pipe includingdie swell) increases.

It is preferred to use lubricant while performing the method accordingto the invention. However, judgement has to be exercised in choosing thesize of the die in relation to the diameter of the liner pipe beforereduction to give the correct clearance between the liner pipe and thepipe to be lined during installation, adequate recovery of the linerpipe diameter, when the load has been removed, must be achieved so as toproduce a final lined pipe in which the liner pipe is a close fit.

The invention is applicable to other grades of polyethylene besides PEXfor example to high density (HDPE) and to medium density (MDPE) grades,as well as to cross-linked polyethylene. It is also applicable topolypropylene. The invention can be applied to line cast iron and steelpipelines, including buried pipelines and installed pipelines. Ingeneral long lengths of pipeline can be lined (eg 200 meters). Theinvention can be used to line steel pipe before the pipes are joined upto make an even greater length and before the pipeline is installed inits final position. Each pipe to be lined in that case can be 150 meterslong, for example.

The standard dimension ratio of the liner pipe may be 33, for example,or a lower value such as SDR 26, 17 or 11 for example, may be used.Standard dimensions ratio means that the quotient obtained by dividingthe outer diameter of the liner pipe L by the wall thickness W.Depending on wall thickness, the final lined pipe may be regarded asequivalent to a stand-alone plastic pipe. In other words, such a pipewould be capable of sustaining the rated pressure of gas, or water orother product to be conducted without any reliance being placed on theoriginal cast iron or steel outer pipe. On the other hand the liner pipemay be merely a liner inserted for purposes of corrosion protection, forexample, but not having the ability to withstand the pressure of theconducted fluid without benefiting from the strength of the surroundingpipe, eg made of steel.

In this specification, the term "liner pipe" means a liner used toproduce either a stand alone plastic pipe or a liner merely housinganti-corrosion or other properties not related to pressure resistance.

We claim:
 1. A method of lining a pipe with a polymer liner comprisespulling the liner through a die to reduce its diameter and through thepipe and on removal of the pulling load allowing the liner to revert toat least the minimum internal diameter of the pipe, the liner having amaximum diameter before the die and a minimum diameter in the die andthe die having an aperture which is symmetrical with respect to acentral, longitudinal axis and comprising in the direction in which theliner is passed, an entry, a throat and an exit, the diameter of theaperture in said direction decreasing over said entry to a minimum atsaid throat and increasing over said exit, the liner having anintermediate diameter after the die and before the liner enters thepipe, the force of pulling being such as partially to restrain die swellof the liner after its emergence from the throat and the liner bendingtowards said axis and in so doing presenting a convex outer surface,when viewed in a sectional plane extending longitudinally of the linerand containing said axis, and then the liner bending away from the axisand in so doing presenting a concave outer surface, when viewed in saidplane, the liner continuously bending through its minimum diameter as itpasses the throat and thereafter undergoing die swell resulting in saidintermediate diameter, which enters the pipe, characterised in that saidentry, when viewed in said plane, is convex over substantially an entireaxial length between where the liner first contacts the die afterbending inwardly and said throat and said liner substantiallycontinuously engages said die over substantially the entire axiallength.
 2. A method according to claim 1 in which the shape of saidaxial length is defined in said plane and in corresponding planes, asthe shape of a circular arc.
 3. A method according to claim 1 in whichsaid axial length of said die engages the whole of said concave outersurface of the liner up to said throat.
 4. In combination apparatus forperforming the method according to claim 1 comprising upstream of thepipe a die having an aperture which is symmetrical with respect to acentral, longitudinal axis and comprising in the direction in which theliner is passed, an entry, a throat and an exit, the diameter of theaperture in said direction decreasing over said entry to a minimum atsaid throat and increasing over said exit, said die being secured to thesurface of the ground or being connected to the leading end of the pipe,guide means for said liner, and downstream of said pipe winch means forexerting a pull on a rope connected to the leading end of liner andguide means for said rope, characterised in that the entry of the die isconvex over an axial length of said die between where the liner firstcontacts the die after bending inwardly and said throat of the die. 5.Apparatus according to claim 4 in which the shape of said axial lengthis defined in a sectional plane extending longitudinally of the linerand containing said axis, and in corresponding planes, as the shape of acircular arc.
 6. Apparatus according to claim 4 in which said axiallength of said die engages the whole of said liner where said diepresents a convex outer surface up to said throat.
 7. A method accordingto claim 2 in which said axial length of said die engages the whole ofsaid concave outer surface of the liner up to said throat.
 8. A methodof lining a pipe with a polymer liner comprises pulling the linerthrough a die to reduce its diameter and through the pipe and on removalof the pulling load allowing the liner to revert to at least the minimuminternal diameter of the pipe, the liner having a maximum diameterbefore the die and a minimum diameter in the die and the die having anaperture which is symmetrical with respect to a central, longitudinalaxis and comprising in the direction in which the liner is passed, anentry, a throat and an exit, the diameter of the aperture in saiddirection decreasing over said entry to a minimum at said throat andincreasing over said exit, the liner having an intermediate diameterafter the die and before the liner enters the pipe, the force of pullingbeing such as partially to restrain die swell of the liner after itsemergence from the throat and the liner bending towards said axis and inso doing presenting a convex outer surface, when viewed in a sectionalplane extending longitudinally of the liner and containing said axis,and then the liner bending away from the axis and in so doing presentinga concave outer surface, when viewed in said plane, the linercontinuously bending through its minimum diameter as it passes thethroat and thereafter undergoing die swell resulting in saidintermediate diameter, which enters the pipe, characterised in that theentry, when viewed in said plane, is convex over an axial length of saiddie between where the liner first contacts the die after bendinginwardly and said throat, wherein the shape of said axial length isdefined in said plane and in corresponding planes, as the shape of acircular arc.
 9. A method as defined in claim 8 in which said axiallength of said die engages the whole of said convex outer surface of theliner up to said throat.
 10. In combination, apparatus for performing amethod of lining a pipe with a polymer liner comprises pulling the linerthrough a die to reduce its diameter and through the pipe and on removalof the pulling load allowing the liner to revert to at least the minimuminternal diameter of the pipe, the liner having a maximum diameterbefore the die and a minimum diameter in the die and the die having anaperture which is symmetrical with respect to a central, longitudinalaxis and comprising in the direction in which the liner is passed, anentry, a throat and an exit, the diameter of the aperture in saiddirection decreasing over said entry to a minimum at said throat andincreasing over said exit, the liner having an intermediate diameterafter the die and before the liner enters the pipe, the force of pullingbeing such as partially to restrain die swell of the liner after itsemergence from the throat and the liner bending towards said axis and inso doing presenting a convex outer surface, when viewed in a sectionalplane extending longitudinally of the liner and containing said axis,and then the liner bending away from the axis and in so doing presentinga concave outer surface, when viewed in said plane, the linercontinuously bending through its minimum diameter as it passes thethroat and thereafter undergoing die swell resulting in saidintermediate diameter, which enters the pipe, characterised in that theentry, when viewed in said plane, is convex over an axial length betweenwhere the liner first contacts the die after bending inwardly and saidthroat, said apparatus comprising upstream of the pipe a die having anaperture which is symmetrical with respect to a central, longitudinalaxis and comprising in the direction in which the liner is passed, anentry, a throat and an exit, the diameter of the aperture in saiddirection decreasing over said entry to a minimum at said throat andincreasing over said exit, said die being secured to the surface of theground or being connected to the leading end of the pipe, guide meansfor said liner, and winch means downstream of said pipe for exerting apull on a rope connected to the leading end of liner and guide means forsaid rope, characterised in that the entry of the die is convex over anaxial length between where the liner first contacts the die afterbending inwardly and said throat of the die wherein said axial lengthengages the whole of said liner where said liner presents a concaveouter surface up to said throat.